Gas-liquid mass transfer : influence of sparger location

The performance of three sparger diameters (DS = 0.6D, DS = D, DS = 1.6D) in combination with three positions (below, above or level with the impeller) for gas-liquid dispersion and mass transfer were evaluated in the case of the Rushton turbine and the A315 propeller in up- or down-pumping mode. The results show that the best results in terms of gas handling and mass transfer capacities are obtained for all impellers with the sparger placed below it and with a diameter at least equal to the impeller diameter. For the sparger position below the agitator, the kLa values of the Rushton turbine are greater than those of the A315 propeller, whatever the pumping mode. The A315 propeller in up-pumping mode is, however, more economically efficient in terms of mass transfer. In all cases, the up-pumping mode gives better results than the down-pumping one

CFD analysis of industrial multi-staged stirred vessels

This paper presents tools for analysis of CFD results adapted for flows in multi-stage stirred vessels through out two industrial cases. Those tanks fitted with double-flow impellers are used first to cool down highly viscous resins and subsequently for indirect emulsification. Since the simulation of these processes in their whole complexity would be unrealistic, it considers single-phase flows without heat transfer. The result analysis in order to prove that the mixing and the circulation are effective is not usual; in these cases, the circulation and impeller numbers are not adapted. The average axial flow numbers are relevant of the circulation in the whole tank and of the connection between the flows produced by the propellers in the given configuration. The velocity profiles give relevant results, but are not sufficient whereas the particle tracking validates that the propellers do not work together in one case and do work together in a second one

Modular simulation and optimization of an 12MW industrial gasifier

In this work, a flexible model, built from elementary modules, is developed for an industrial waste gasification process, in an industrial moving bed reactor located in Morcenx (France). This gasifier is able to treat more than 46,875 ton/year of RDF (Refused Derived Fuel) waste for producing 12 MW. Drying, pyrolysis, combustion / gasification and plasma polishing are used to convert waste directly into a synthesis gas composed of carbon monoxide and hydrogen. This synthesis gas is then used for producing electricity via gas engine

Gas-liquid mass transfer : a comparison of down-and up-pumping axial flow impellers with radial impellers

The performance of a down- and up-pumping pitched blade turbine and A315 for gas-liquid dispersion and mass transfer was evaluated and then compared with that of Rushton and Scaba turbines in a small laboratory scale vessel. The results show that when the axial flow impellers are operated in the up-pumping mode, the overall performance is largely improved compared with the down-pumping configuration. Compared with the radial turbines, the up-pumping A315 has a high gas handling capacity, equivalent to the Scaba turbine and is economically much more efficient in terms of mass transfer than both turbines. On the other hand, the uppumping pitched blade turbine is not as well adapted to such applications. Finally, the axial flow impellers in the down-pumping mode have the lowest performance of all the impellers studied, although the A315 is preferred of the pitched blade turbine

Effect of Tween 80 on bubble size and mass transfer in a bubble contactor

Gas absorption in aqueous solutions with Tween 80 and absorption processes based on hydrodynamics and mass transfer is determined. The impact of surfactant concentration on gas holdup and gas-liquid interfacial area is analyzed, observing an increase of these parameters with surfactant concentration. The influence of liquid-phase contamination on the absorption process is investigated on the basis of the liquid-film mass transfer coefficient, removing the effect caused by the presence of a surfactant and the gas flow rate on the interfacial area and, thereby, on the volumetric mass transfer coefficient. The opposite effect on the mass transfer coefficient can be observed which decreases in the presence of the surfactant

Modelling of krypton-xenon separation by dynamic fixed-bed adsorption on zeolite

International audienceCurrently noble gases are separated by cryogenic distillation, which is an expensive process with safety constraints due to the cryogenic temperatures used. Adsorptive separation, such as temperature/pressure swing adsorption, is studying as it is considered as an energy, safety and cost effective alternative. Different selective materials are described in the literature from inorganic adsorbents based on physical adsorption to new metal-organic frameworks (MOFs) based on size and chemistry. This work focuses on the description of a modelling of Kr-Xe separation by selective adsorption on a chabazite zeolite in a fixed bed column

Study of gas-liquid mixing in stirred vessel using electrical resistance tomography

This study presents a full operation and optimisation of a mixing unit; an innovative approach is developed to address the behaviour of gas-liquid mixing by using Electrical Resistance Tomography (ERT). The validity of the method is investigated by developing the tomographic images using different numbers of baffles in a mixing unit. This technique provided clear visual evidence of better mixing that took place inside the gasliquid system and the effect of a different number of baffles on mixing characteristics. For optimum gas flow rate (m3/s) and power input (kW), the oxygen absorption rate in water was measured. Dynamic gassingout method was applied for five different gas flow rates and four different power inputs to find out mass transfer coefficient (KLa). The rest of the experiments with one up to four baffles were carried out at these optimum values of power input (2.0 kW) and gas flow rate (8.5×10-4 m3/s). The experimental results and tomography visualisations showed that the gasliquid mixing with standard baffling provided near the optimal process performance and good mechanical stability, as higher mass transfer rates were obtained using a greater number of baffles. The addition of single baffle had a striking effect on mixing efficiency and additions of further baffles significantly decrease mixing time. The energy required for complete mixing was remarkably reduced in the case of four baffles as compared to without any baffle. The process economics study showed that the increased cost of baffles installation accounts for less cost of energy input for agitation. The process economics have also revealed that the optimum numbers of baffles are four in the present mixing unit and the use of an optimum number of baffles reduced the energy input cost by 54%

Hydrodynamique induite par un oxygénateur de surface (influence du design des agitateurs sur la qualité de la dispersion)

Le turboxal TM est un nouveau système d'agitation flottant conçu pour oxygéner et brasser les bassins d'épuration biologique des eaux. Il comprend trois agitateurs entourés d'une volute fixe comportant six chicanes. L'objectif est d'améliorer les performances c'est à dire augmenter le débit de gaz injecté tout en maintenant un transfert de matière correct. L'analys, à la fois expérimentale et numérique, du fonctionnement a fait ressortir que les performances ne pouvaient être accrues par de simples modifications géométriques. Le deuxième point de ce travail a alors porté sur la recherche par simulation numérique d'une nouvelle géométrie de la turbine remplaçant à la fois la turbine existante et l'hélice à refoulement vers le haut. 3 turbines modifiées ont été sélectionnées et testées expérimentalement au sein du Turboxal TM. Finalement un Turboxal TM de 2ème génération permettant de satisfaire notre objectif a été proposé.TOULOUSE-ENSIACET (315552325) / SudocSudocFranceF

Les agitateurs auto-aspirants. Partie I : Présentation et principe de fonctionnement

Dans le domaine des réactions gaz-liquide, les agitateurs auto-aspirants sont employés car de par leur capacité à aspirer le gaz ils permettent de se passer des pompes ou compresseurs de recyclage. Ceci commence à être transposé dans le domaine du traitement biologique des eaux usées industrielles ou urbaines pour pouvoir injecter de l'oxygène et non pas de l'air. En prélude à une étude portant sur un nouveau système auto-aspirant justement utilisé dans le domaine du traitement de l'eau, ils nous a paru utile de lister les technologies existantes avec leur mode de fonctionnement. Nous avons également inclus dans cette première partie un guide de choix entre les différentes technologies de mobiles auto-aspirants en fonction de l'application considérée